DE 10 2007 024 525 B4 describes a device in which three cameras are used to perform a visual assessment of defects in the edge region of a wafer. For recording defects, one camera is positioned opposite the edge region above the wafer and one camera is positioned opposite the edge region below the wafer. A third camera is disposed opposite the edge region of the wafer in radial direction. The edge region of the wafer captured by the cameras is illuminated by a homogeneous, diffusely radiating illumination, and pictures are taken by the camera and displayed to a user of the device on a monitor for visual evaluation. Thus it is possible when capturing and using the exact position of a defect on the wafer that subjective assessments of the defects can also be made. An objective, qualitative assessment of defects is not possible in this device.
In an edge checking device disclosed in DE 11 2008 000 723 T5, test results are displayed depending on the edge information acquired from the inspected wafer. For this purpose, the circumferential surface of a wafer is captured from three recording directions by at least one CCD line camera. The axes of the three image recordings intersect in the center plane of the wafer at a point close to the circumferential surface of the wafer so that one viewing direction is directed to the outer circumferential surface and the other two image recordings are directed, respectively, to the beveled circumferential edges of the wafer. The configuration of the illumination needed for image capture was not disclosed. The captured images are displayed on a display device for manual evaluation and the position-dependent edge information is stored in a storage unit. Further, edge information is stored in a storage unit depending on position based on changes in shading in the captured image content. The acquired data are preferably displayed visually in the form of a profile curve on the basis of which a statistical evaluation of the edge information is made possible so that a trend in the overall shape can be determined therefrom. This has the drawback that image defects caused, for example, by reflected light at trouble spots or by improperly angled edge regions when making photographic recordings of a small segment of the edge region of a wafer by means of CCD line cameras can lead to erroneous interpretations of the actual edge shape, can corrupt measurement results or even render measurement impossible.